The present invention relates to raw sheet material for use in the manufacture of packaging and, in particular, it concerns a multi-layer sheet material in which a one-way valve is integrally formed by the bonding together of the layers to form the sheet material.
It is known to provide packaging material that include a means for creating a pressure differential inside a container formed of such material such as bags. That majority of such containers are designed to create a vacuum state within the container in order to preserve the contents. However, such means currently in use in the art are separate valve structures that are added to the sheet material of the container at the time of manufacture.
It will be readily understood that the inclusion of such valve means adds considerable cost to the manufacturing of these packaging containers.
There is therefore a need for a multi-layer sheet material in which a one-way valve is integrally formed by the bonding together of the layers to form the sheet material.